A communication system is a facility that enables communication between two or more entities such as user terminal equipment and/or network entities and other nodes associated with a communication system. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on.
The communication may be provided by a fixed line and/or wireless communication interfaces. A feature of wireless communication systems is that they provide mobility for the users thereof. An example of communication systems providing wireless communication is a public land mobile network (PLMN). An example of the fixed line system is a public switched telephone network (PSTN).
A communication system typically operates in accordance with a given standard or specification which sets out what the various elements of a system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely user equipment, is provided with a circuit switched server or a packet switched server or both. Communication protocols and/or parameters which should be used for the connection are also typically defined. For example, the manner how communication shall be implemented between the user equipment and the elements of the communication networks is typically based on a predefined communication protocol. In other words, a specific set of “rules” on which the communication can be based needs to be defined to enable the user equipment to communicate via the communication system.
The introduction of Third Generation (3G) communication systems will significantly increase the possibilities for accessing services on the Internet via mobile user equipment (UE) as well as other types of UE.
Various user equipment (UE) such as computers (fixed or portable), mobile telephones, personal data assistants or organisers and so on are known to the skilled person and can be used to access the Internet to obtain services. Mobile user equipment referred to as a mobile station (MS) can be defined as a means that is capable of communication via a wireless interface with another device such as a base station of a mobile telecommunication network or any other station.
The term “service” used above and hereinafter will be understood to broadly cover any service or goods which a user may desire, require or be provided with. The term also will be understood to cover the provision of complimentary services. In particular, but not exclusively, the term “service” will be understood to include Internet protocol multimedia IM services, conferencing, telephony, gaming, rich call, presence, e-commerce and messaging e.g. instant messaging. A “service” may comprise two or more parts. For example, a video telephone service comprises a voice part and a video part. Alternatively two or more services may be provided at the same time, for example a gaming service and a chatroom service may be provided at the same time.
The 3G Partnership Project (3GPP) is defining a reference architecture for the Universal Mobile Telecommunication System (UMTS) core network which will provide the users of user equipment UE with access to these services. This UMTS core network is divided into three principal domains. These are the Circuit Switched domain, the Packet Switched domain and the Internet Protocol Multimedia (IM) domain.
The latter of these, the IM domain, makes sure that multimedia services are adequately managed. The IM domain supports the Session Initiation Protocol (SIP) as developed by the Internet Engineering Task Force (IETF).
In prepaid schemes, when a service or services are being requested, the S-CSCF/SCF (serving call session control function/session charging functions) requests a quota (allocation of money which has been prepaid) from the Online Charging System (OCS). The S-CSCF/SCF sends all the service information required to rate the service. In the case of a SIP session, all the SDP (Session Description Protocol) information such as media type, media codec etc. are sent to the OCS. If the account cannot cover the cost of the service or services requested, the OCS instructs the S-CSCF/SCF to release the ongoing session. However, the account may have sufficient fund in it to pay for a subset of the requested medias, for instance if a video call (voice and video) is requested the account may cover the cost for the voice component only. Nevertheless, with the current proposals the session will be released.